Liquid fuel supply pumps useful for liquid fuel combustion apparatus generally comprise a cylinder B disposed in a solenoid A and a plunger C supported within the cylinder B by an upper spring D and a lower spring E and movable upward and downward, as shown in FIG. 1.
A power supply of modulated pulse width is connected to the solenoid A to intermittently drive the plunger C up and down and supply liquid fuel to a liquid fuel combustion apparatus at a rate of about 5 cc to 8 cc/min.
However, with the wide use of space heaters, it has been strongly desired in recent years to give a variable heat output over a wider range than heretofore possible for more delicately controlled comfortable space heating or for savings in energy.
However, when giving a heat output which is variable, for example, from 3500 Kcal/h to 1000 Kcal/h, the supply of liquid fuel by the pump shown in FIG. 1, which is 5 cc to 8 cc/min, must be reduced to not larger than 1/3 the amount, i.e. 1 to 3 cc/min. To give a still smaller heat output, the supply must be reduced further.
Nevertheless, when for example obtaining a heat output of 3500 Kcal/h by driving the plunger C at a pulse frequency of 10 Hz, the plunger output per stroke must be ##EQU1## Since the flow rate of the pump of FIG. 1 is limited to the range of 5 cc/min in view of accuracy, it is impossible to obtain the above variable range of low heat outputs.
Further gear pumps involve a lower limit of as much as 30 cc/min due to the leakage of the fluid through the gear-to-gear clearance. The gear pump thus also fails to give the above variable range of low heat output.